Occupancy sensors, also called motion sensors or proximity detectors, detect if people are near the sensor. Typical sensors use passive infrared (PIR) technology. These detect infrared energy from moving objects. An example of this kind of sensor is the ZMOTION Detection Module from Zilog of Milpitas, Calif. Some sensors merely detect the presence of people (or objects confused with people). Other sensors may detect the distance from the sensor to the person or give other information about their location or direction of travel. Another type of sensor is an active infrared (IR) sensor with an emitter and receiver that detects reflections or interruptions of emitted IR radiation. Other sensors include ultrasonic proximity sensors, sound source localization sensors and sensing using computer vision.
A typical use of occupancy sensors is lighting control to automatically turn lights on and off. When used for this purpose, a sensor detects light and may also be used to disable lights automatically when another light source, for example daylight, is present. The primary benefit of using sensors for this purpose is to save power (to use less electricity) by turning off a light when it is not needed. In addition to lights, displays and other local devices can be controlled to save energy.
Another typical use of occupancy sensors is for intrusion detection as a part of a burglar alarm or other (physical) security system.
Sensors have been used for other purposes. For example, in some systems, sensors are used to control projectors. If an object (person) is detected within a minimum distance, the projector's output light intensity is reduced or the projector is turned off to avoid shining too much light into a person's eyes. In particular, these systems may be a mobile device that uses a laser projector. In some systems, a projector is also turned off if no one is detected in the area.
In some systems, sensors are used to control retail terminals such as kiosks. Sensors are used to detect if a person is proximate to the kiosk, approaching the kiosk or walking by the kiosk. The sensors are used to log traffic patterns with respect to the kiosk. The sensors trigger powering down a kiosk (causing it to be in a low power or energy saving mode) when no one is nearby. The sensor triggers playing a sound when someone walks by the kiosk. Some Kiosks handle sensitive information for brief periods of time. For example, some kiosks handle credit card payments. Avoiding data loss is not important for these kiosks since the sessions using sensitive information are short enough that interruption is infrequent and of a character such that they can be abandoned or restarted from the beginning if interrupted.
Screen savers or screen lock programs detect the lack of user interface (UI) activity (idle time) and lock a computer by taking over (disabling) the UI. Some screen savers also use time of day for determining when to activate. The normal display is replaced by an alternative display (sometimes to a dynamic display to avoid damage due to long term static display, sometimes to provide entertainment). While in this mode, user input devices such a keyboard and mouse no longer send events to running applications but instead are used to exit screen saver mode (either on any activity or on successfully entering a password or PIN). Except for the being disconnected from the UI, running application software and local storage are unaffected by the screen saver.
Some live teleconferencing, video conferencing or meeting recording systems track people. For example, sound source localization (SSL) is used to track a person who is speaking. The pan, zoom and/or tilt of a camera are controlled, a portion of the output of an omnidirectional video camera is selected or one of multiple cameras is selected to capture video of the person talking. Video from cameras is used for determining when people enter or exit a meeting room. When a person enters or exits, a camera view that shows the person is selected.
Logging out is important after people are done using computers at internet cafes and other public computers. Each period of use is a session. Some software used for this purpose ends the session based on a user action, such as the user logging off, shutting down the system or pressing a “log off” button, based on idle time (e.g., when a screen saver starts) or based on a network disconnect. Some software used for this purpose clears browser URL history and temporary files when a session ends. Some software automatically enables internet access on login and disables access on logout. Some software causes reboot, causes shutdown, closes programs used (closes all running applications), logs off the user or locks the terminal at the end of a session.
In grid computing (also referred to as volunteer computing or global computing), a personal computer runs a program (a computing application) for others while that computer would otherwise be idle. Some grid computing software appears to be a screen saver to a local user. Some software can be configured to consider a computer as not idle if a user that runs batch jobs is logged in. Some software is implemented as a system service so it runs when a no user is logged in.
There are a number of security and reliability concerns in grid computing. Some software saves intermediate results to minimize losses in case of a system crash.